[Paper Review] Cosmological viability of a double field unified model from warm inflation

Rocco D’Agostino, Orlando Luongo|arXiv (Cornell University)|Dec 23, 2021

Cosmology and Gravitation TheoriesPhysics and Astronomy51 references36 citations

TL;DR

This paper proposes a double scalar field (DSF) model unifying inflation, dark matter, and dark energy within a warm inflation framework, using non-standard kinetic terms and exponential potentials. Bayesian analysis with Planck, Pantheon SNe Ia, and Hubble data shows the model fits current observations as well as ΛCDM, with constrained parameters within theoretical ranges and stable late-time dynamics.

ABSTRACT

In this paper, we investigate the cosmological viability of a double scalar field model motivated by warm inflation. To this end, we first set up the theoretical framework in which dark energy, dark matter and inflation are accounted for in a triple unification scheme. We then compute the overall dynamics of the model, analyzing the physical role of coupling parameters. Focussing on the late-time evolution, we test the model against current data. Specifically, using the low-redshift Pantheon Supernovae Ia and Hubble cosmic chronometers measurements, we perform a Bayesian analysis through the Monte Carlo Markov Chains method of integration on the free parameters of the model. We find that the mean values of the free parameters constrained by observations lie within suitable theoretical ranges, and the evolution of the scalar fields provides a good resemblance to the features of the dark sector of the universe. Such behaviour is confirmed by the outcomes of widely adopted selection criteria, suggesting a statistical evidence comparable to that of the standard $\Lambda$CDM cosmology. We finally discuss the presence of large uncertainties over the free parameters of the model and we debate about fine-tuning issues related to the coupling constants.

Motivation & Objective

• To develop a cosmological model that unifies inflation, dark matter, and dark energy using a double scalar field framework.
• To explore the viability of a warm inflation scenario where the inflaton field survives as dark matter and drives late-time acceleration.
• To test the model against current low-redshift observational data, including Type Ia supernovae and cosmic chronometers.
• To assess the stability and dynamical behavior of the model in the late-time universe using critical point analysis.
• To evaluate the statistical significance of the model relative to the standard ΛCDM paradigm through Bayesian model comparison.

Proposed method

• Formalism is built on a double scalar field Lagrangian with non-standard kinetic term for ψ and exponential coupling to ϕ: $ \mathcal{L} = \frac{1}{2}(\nabla\phi)^2 + \frac{1}{2}e^{-\kappa\lambda\phi}(\nabla\psi)^2 + e^{-\kappa\mu\phi}V(\psi) $.
• The potential $ V(\psi) = V_0 + \frac{1}{2}m^2\psi^2 $ is used to model chaotic inflation and late-time dark energy behavior.
• Dynamical systems analysis is applied to study the late-time evolution and stability of critical points.
• Monte Carlo Markov Chain (MCMC) method is used to perform Bayesian inference on free parameters using Pantheon SNe Ia and Hubble parameter data.
• Model selection criteria (AIC, BIC) are applied to compare the DSF model with ΛCDM in terms of statistical evidence.
• The model is tested for consistency with observational constraints on the Hubble parameter and dark energy equation of state.

Experimental results

Research questions

• RQ1 Can a double scalar field model based on warm inflation successfully unify inflation, dark matter, and dark energy in a single theoretical framework?
• RQ2 How do the coupling parameters λ and μ affect the late-time dynamics and stability of the scalar fields?
• RQ3 To what extent does the DSF model fit current low-redshift cosmological data (Pantheon SNe Ia and Hubble measurements)?
• RQ4 Does the DSF model achieve a statistical fit comparable to the standard ΛCDM model?
• RQ5 What are the implications of large uncertainties in the model’s free parameters, and how do they relate to fine-tuning issues?

Key findings

• The Bayesian MCMC analysis constrains the free parameters (λ, μ, m, V₀) to values within theoretically acceptable ranges, supporting the model's physical viability.
• The late-time evolution of the scalar fields in the DSF model closely mimics the observed features of the dark sector, including dark energy dominance and matter-radiation transition.
• The model achieves a statistical fit comparable to ΛCDM, as confirmed by AIC and BIC selection criteria, indicating no significant statistical preference for ΛCDM.
• Critical point analysis confirms the stability of the late-time attractor solution, supporting the model’s long-term dynamical consistency.
• Despite good observational fit, the model exhibits large uncertainties in the coupling parameters λ and μ, suggesting potential fine-tuning issues.
• The presence of thermal fluctuations in warm inflation provides a natural mechanism for generating primordial perturbations and linking the inflaton to dark matter relics.